Positive active material for rechargeable lithium battery, preparing method thereof and rechargeable lithium battery comprising positive electrode including positive active material

ABSTRACT

A positive active material for a rechargeable lithium battery includes a first positive active material including a secondary particle including at least two agglomerated primary particles, where at least one part of the primary particles has a radial arrangement structure, as well as a second positive active material having a monolith structure. The first and second positive active materials may both include nickel-based positive active materials. A method of preparing the positive active material, and a rechargeable lithium battery including a positive electrode including the positive active material are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2017-0165431, filed in the Korean IntellectualProperty Office on Dec. 4, 2017; and Korean Patent Application No.10-2018-0153649, filed in the Korean Intellectual Property Office onDec. 3, 2018, the entire content of each of which is incorporated hereinby reference.

BACKGROUND 1. Field

One or more aspects of example embodiments of the present disclosure arerelated to a positive active material for a rechargeable lithiumbattery, a preparing method thereof, and a rechargeable lithium batteryincluding a positive electrode including the same.

2. Description of the Related Art

As portable electronic devices, communication devices, and/or the likeare developed, there is a need for development of a rechargeable lithiumbattery having a high energy density.

A positive active material of a rechargeable lithium battery may be alithium nickel manganese cobalt composite oxide, a lithium cobalt oxide,and/or the like. When such positive active materials are used, thecycle-life of a rechargeable lithium battery may be decreased,resistance may be increased, and capacity characteristics may beinsufficient due to cracks generated in the positive active material ascharging and discharging are repeated.

SUMMARY

One or more aspects of example embodiments of the present disclosure aredirected toward a positive active material for a rechargeable lithiumbattery having improved stability and electrochemical characteristicsdue to decreased residual lithium, as well as a preparing methodthereof.

One or more example embodiments of the present disclosure are directedtoward a rechargeable lithium battery having improved cell stability byincluding a positive electrode including the positive active materialfor a rechargeable lithium battery.

One or more example embodiments of the present disclosure provide apositive active material for a rechargeable lithium battery including afirst positive active material including a secondary particle includingat least two agglomerated primary particles, where at least one part ofthe primary particles (e.g., each of the primary particles) has a radialarrangement structure; and a second positive active material having amonolith structure, wherein both of the first positive active materialand the second positive active material are or include a nickel-basedpositive active material.

One or more example embodiments of the present disclosure provide amethod of preparing a positive active material for a rechargeablelithium battery that includes subjecting a first precursor to a firstheat-treatment in an oxidizing gas atmosphere to obtain a firstnickel-based oxide, subjecting a second precursor to a secondheat-treatment in an oxidizing gas atmosphere to obtain a secondnickel-based oxide, mixing the first nickel-based oxide and the secondnickel-based oxide, and subjecting the mixture to a third heat-treatmentin an oxidizing gas atmosphere to obtain a positive active materialincluding a first positive active material and a second positive activematerial, wherein the second nickel-based oxide includes particleshaving a monolith structure.

One or more example embodiments of the present disclosure provide arechargeable lithium battery including a positive electrode includingthe positive active material for a rechargeable lithium battery, anegative electrode, and an electrolyte between the positive electrodeand the negative electrode.

One or more example embodiments of the present disclosure may provide apositive active material for a rechargeable lithium battery havingdecreased or reduced residual lithium and excellent stability andelectrochemical characteristics, and a method for producing the same.

One or more example embodiments of the present disclosure may provide arechargeable lithium battery including the positive active material fora rechargeable lithium battery and having improved cell stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing shapes of the primary particlesaccording to embodiments of the present disclosure,

FIG. 2 is a schematic view describing a radial shape of a secondaryparticle according to embodiments of the present disclosure,

FIG. 3 is a schematic view showing a cross-sectional structure of asecondary particle according to embodiments of the present disclosure,and

FIG. 4 is a schematic view showing a structure of a rechargeable lithiumbattery including a positive electrode including a positive activematerial for a rechargeable lithium battery according to embodiments ofthe present disclosure.

DETAILED DESCRIPTION

The present disclosure will be described more fully hereinafter withreference to the accompanying drawings, in which example embodiments ofthe present disclosure are shown. As those skilled in the art wouldrealize, the described embodiments may be modified in various differentways, all without departing from the spirit or scope of the presentdisclosure. The drawings and description are to be regarded asillustrative in nature and not restrictive. Like reference numeralsdesignate like elements throughout the specification, and duplicativedescriptions thereof may not be provided.

The thicknesses of layers, films, panels, regions, etc., may beexaggerated in the drawings for clarity. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening element(s) may also be present. In contrast, when an elementis referred to as being “directly on” another element, no interveningelements are present. Expressions such as “at least one of”, “one of”,“selected from”, “at least one selected from”, and “one selected from”,when preceding a list of elements, modify the entire list of elementsand do not modify the individual elements of the list. Further, the useof “may” when describing embodiments of the present disclosure refers to“one or more embodiments of the present disclosure.”

The sizes or particle diameters of various particles may be representedby a single measurement to show an average size of a group of particles.Generally used methods of reporting particle sizes include a modediameter showing the maximum value of the particle size distribution(e.g., most common particle size within the distribution), a mediandiameter corresponding to the integral center value of the particle sizedistribution curve, one or more average diameters (e.g., numeralaverage, length average, area average, mass average, volume average,etc.), and/or the like. Unless otherwise specified, the average sizes oraverage particle diameters as reported in this disclosure refer tonumeral average sizes or numeral average diameters, and may be obtainedby measuring D50 (the particle diameter at the 50th percentile of theparticle size distribution).

In some embodiments, the term “monolith structure” may refer to astructure in which the morphology of each particle is separated and/ordispersed from each other as mutually distinguishable independentphases.

Hereinafter, referring to FIGS. 1 to 3, a positive active material for arechargeable lithium battery according to embodiments of the presentdisclosure is described.

A positive active material for a rechargeable lithium battery accordingto embodiments of the present disclosure includes a first positiveactive material including a secondary particle including at least twoagglomerated primary particles, and a second positive active materialhaving a monolith structure. At least one part of the secondary particlemay have a radial arrangement structure, and both of the first positiveactive material and the second positive active material may be orinclude a nickel-based positive active material.

Hereinafter, the first positive active material according to embodimentsof the present disclosure is described.

The first positive active material may include a secondary particleincluding at least two agglomerated primary particles. At least one partof the primary particles (e.g., each of the primary particles) may havea plate shape. Each of the primary particles may have a thickness thatis smaller than a long-axis length, e.g., length of its longest axis(e.g., plane direction long-axis). For example, the “long-axis length”may refer to a maximum length of the largest surface of the primaryparticles. For example, the primary particles may have a structure wherea length or thickness (t) in one direction (i.e., thickness direction)is smaller than a long-axis length (a) in another direction (i.e., planedirection).

FIG. 1 is a schematic view showing one or more suitable shapes of theprimary particles according to embodiments of the present disclosure.

Referring to FIG. 1, a primary particle according to embodiments of thepresent disclosure may have any suitable shape, such as (A) a polygonalnanoplate shape (such as hexagon and/or the like), (B) a nanodisk shape,and/or (C) a rectangular parallelepiped shape, each having a basicplate-shaped structure.

The thickness t of the primary particles may be smaller than the planedirection lengths a and b. The length a in the plane direction may belarger than b, or may be the same as b. In some embodiments, in theprimary particles, the direction in which the thickness t is defined maybe referred to as a thickness direction, and the directions includingthe lengths a and b may be referred to as plane directions.

The first positive active material according to embodiments of thepresent disclosure may have irregular porous pores in the internal partand/or in the external part of the secondary particle. The term“irregular porous structure” may refer to a structure in which the poresizes and shapes are not regular and do not have uniformity. Theinternal part of the irregular porous structure may include primaryparticles similar or substantially identical to those in the externalpart thereof. The primary particles in the internal part of thesecondary particle may be arranged without regularity, unlike theprimary particles in the external part.

The term “external part” may refer to a region (e.g., of the particle)within about 30 length % to about 50 length % from the outermostsurface, for example, within about 40 length % from the outermostsurface with respect to the distance from the center to the surface ofthe secondary particle, or in some embodiments, may refer to a regionwithin about 2 μm from the outermost surface of the secondary particle.The term “internal part” may refer to a region (e.g., of the particle)within about 50 length % to about 70 length % from the center, forexample, within about 60 length % from the center with respect to thedistance from the center to the surface of the secondary particle, or insome embodiments, a region excluding the region within about 2 μm fromthe outermost surface of the secondary particle.

The secondary particle of the first positive active material accordingto embodiments of the present disclosure may include an open pore in thecenter of the internal part with a size of less than about 150 nm, forexample, about 10 nm to about 148 nm. The open pore may be an exposedpore into which an electrolyte solution may flow in and out. In someembodiments, the open pore may be formed at a depth of less than orequal to about 150 nm, for example, about 0.001 nm to about 100 nm, orabout 1 nm to about 50 nm, on average, from the surface of the secondaryparticle.

The first positive active material according to embodiments of thepresent disclosure may include a secondary particle formed by arrangingthe long axes of at least one part of the primary particles in a radialdirection. At least one part of the primary particles may have a radialarrangement. For example, each of the primary particles may have a plateshape, and a long-axis of at least one part of the primary particles(e.g., the external part) may be arranged in a radial direction. FIG. 2is a schematic view describing a radial shape of a secondary particleaccording to embodiments of the present disclosure.

A “radial” arrangement structure refers to a structure in which thethickness (t) direction of the primary particles are arrangedperpendicular to or within an angle of about ±5° of perpendicular withrespect to the direction (R) toward the center of the secondaryparticles, as shown in FIG. 2.

The average length of the primary particles of the secondary particlemay be about 0.01 μm to about 5 μm. For example, the average length maybe about 0.01 μm to about 2 μm, about 0.01 μm to about 1 μm, about 0.02μm to about 1 μm, or about 0.05 μm to about 0.5 μm. Herein, the term“average length” refers to an average of the average long-axis lengthand the average short-axis length in the plane direction of the primaryparticles, or an average particle diameter when the primary particleshave a spherical shape.

An average thickness of the primary particles of the secondary particlemay be, for example, greater than or equal to about 50 nm, greater thanor equal to about 100 nm, greater than or equal to about 200 nm, greaterthan or equal to about 300 nm, greater than or equal to about 400 nm,greater than or equal to about 500 nm, greater than or equal to about600 nm, greater than or equal to about 700 nm, greater than or equal toabout 800 nm, greater than or equal to about 900 nm, greater than orequal to about 1 μm, greater than or equal to about 1.2 μm, greater thanor equal to about 1.4 μm, and for example, less than or equal to about13 μm, less than or equal to about 12 μm, less than or equal to about 11μm, less than or equal to about 10 μm, less than or equal to about 9 μm,less than or equal to about 8 μm, less than or equal to about 7 μm, lessthan or equal to about 6 μm, less than or equal to about 5 μm, less thanor equal to about 4 μm, less than or equal to about 3 μm, or less thanor equal to about 2 μm. A ratio between the average thickness and theaverage length may be about 1:1 to about 1:10, for example about 1:1 toabout 1:8, or about 1:1 to about 1:6.

As described above, when the average length, the average thickness, andthe ratio between the average thickness and the average length of theprimary particles satisfy the above ranges, a relatively large number oflithium diffusion paths between surface grain boundaries and crystalsurfaces capable of transferring lithium to the external part of thesecondary particle may be exposed, such that lithium diffusivity may beimproved, and high initial efficiency and capacity may be enabled, whenthe sizes of the primary particles are sufficiently small and theprimary particles are radially arranged in the external part (e.g., ofthe secondary particle). When the primary particles are arrangedradially, the pores exposed at the surface between the primary particlesmay be directed toward the center direction (e.g., of the secondaryparticle), thereby promoting lithium diffusion from the surface. Whenlithium is deintercalated and/or intercalated into the radially arrangedprimary particles, substantially uniform shrinkage and expansion may beenabled, and the presence of pores in a (001) direction, along whichparticles expand during lithium intercalation, may alleviate stresscaused by expansion. The probability of cracks occurring duringshrinkage and expansion may be lowered due to the small sizes of theplate-shaped primary particles, and the pores in the internal part ofthe secondary particle may additionally alleviate stress caused by thevolume changes, thereby decreasing crack generation between the primaryparticles during charging and discharging, improving cycle-lifecharacteristics, and reducing a resistance increase.

Closed pores may be present in the internal part of the secondaryparticle, and closed pores and/or open pores may be present in theexternal part of the secondary particle. The closed pores may exclude ormostly exclude an electrolyte, while the open pores may include anelectrolyte therein. Each closed pore may be an independent pore formedby closing the wall surfaces of the pore so that they are not connectedto other pores; while the open pores may be formed as continuous poresconnected to the outside of the particles when at least one part of eachpore wall is formed to be an open structure.

The positive active material for a rechargeable lithium batteryaccording to embodiments of the present disclosure may minimize orreduce direct contact between the cracked surface and the electrolytesolution even when cracks are generated, thereby suppressing an increaseof a sheet resistance, due to the first positive active material asdescribed above.

FIG. 3 is a schematic view showing a cross-sectional structure of asecondary particle according to embodiments of the present disclosure.

Referring to FIG. 3, the secondary particle 11 includes an external part14 in which the plate-shaped primary particles are arranged in a radialdirection and an internal part 12 where primary particles areirregularly arranged.

In the internal part 12, a larger amount of empty voids between theprimary particles may be present compared to within the external part.The pore sizes and porosity in the internal part may be larger and moreirregular than those in the external part. In FIG. 3, the arrowindicates a direction of lithium ion movement (e.g., duringintercalation).

The secondary particle according to embodiments of the presentdisclosure may have a porous structure in the internal part, so that adiffusion distance of lithium ions to the internal part of the secondaryparticle may be decreased, and the external part of the secondaryparticle may be radially arranged toward the surface, so that lithiumions are easily intercalated into the surface. In some embodiments, thesizes of the primary particles of the positive active material for arechargeable lithium battery are small so that it is easy to secure alithium transfer path between the crystal grains. In some embodiments,the sizes of the primary particles are small and the pores betweenprimary particles alleviate volume changes that occur during chargingand discharging, minimizing or reducing particle stress when the volumechanges during charging and discharging.

An average particle diameter of the secondary particle of embodiments ofthe present disclosure may be about 1 μm to about 20 μm. For example, itmay be about 0.05 μm to about 10 μm, about 1 μm to about 10 μm, or about5 μm to about 15 μm. For example, it may be about 1 μm to about 5 μm, orabout 10 μm to about 20 μm.

The secondary particle according to embodiments of the presentdisclosure may include radial primary particles and non-radial primaryparticles. An amount of the non-radial primary particles may be lessthan or equal to about 20 wt %, about 0.01 wt % to about 10 wt %, orabout 0.1 wt % to about 5 wt % based on a total of 100 wt % of theradial primary particles and non-radial primary particles together. Whenthe non-radial primary particles are included in the above range inaddition to the radial primary particles within the secondary particle,a rechargeable lithium battery having improved cycle-lifecharacteristics due to easy diffusion of lithium may be manufactured.

Hereinafter, a second positive active material according to embodimentsof the present disclosure is described.

The second positive active material according to embodiments of thepresent disclosure may have a monolith structure. For example, thesecond positive active material may include or have a form in which aplurality of crystal particles are separated and/or dispersed so as toform independent and/or separated phases for each of the particlesrather than a coagulated form, but two or three particles may beattached to each other.

The shape of the second positive active material is not particularlylimited, and may have a random shape (such as a sphere, an oval, aplate-shape, and/or a rod).

The second positive active material according to embodiments of thepresent disclosure may be included in an amount of about 10 wt % toabout 50 wt % based on a total weight of the positive active materialfor a rechargeable lithium battery. For example, the second positiveactive material may be included in an amount of greater than or equal toabout 10 wt %, greater than or equal to about 15 wt %, greater than orequal to about 20 wt %, or greater than or equal to about 25 wt %, andfor example, less than or equal to about 50 wt %, less than or equal toabout 45 wt %, less than or equal to about 40 wt %, or less than orequal to about 35 wt %. When the second positive active material havinga monolith structure is included within these ranges, residual lithiumcompounds remaining in the positive active material after synthesis ofthe active material may be minimized or reduced.

As described above, the second positive active material may have amonolith structure, and thereby a residual lithium concentration in thepositive active material for a rechargeable lithium battery according toembodiments of the present disclosure may be, for example, less than orequal to about 1200 ppm, less than or equal to about 1100 ppm, less thanor equal to about 1000 ppm, less than or equal to about 990 ppm, lessthan or equal to about 980 ppm, or less than or equal to about 970 ppm.Accordingly, the nickel-based active material having a large nickelcontent may secure a low residual lithium concentration within theseranges.

In some embodiments, the primary particles in the first positive activematerial and the second positive active material may each have asuitable size. An average particle diameter of the second positiveactive material may be about 0.05 μm to about 10 μm. For example, it maybe about 0.1 μm to about 10 μm. For example, it may be about 0.1 μm toabout 5 μm. In this way, the primary particles of the first positiveactive material and the second positive active material may each have asuitable size, so that a density of the positive active material for arechargeable lithium battery according to embodiments of the presentdisclosure may be further increased.

The first positive active material according to embodiments of thepresent disclosure and the second positive active material may eachindependently be or include a nickel-based positive active materialrepresented by Chemical Formula 1:Li_(a)(Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z))O₂,  Chemical Formula 1

wherein, in Chemical Formula 1, M is an element selected from boron (B),magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium(Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium(Zr), and aluminum (Al), and

0.95≤a≤1.3, x≤(1-x-y-z), y≤(1-x-y-z), 0<x<1, 0≤y<1, and 0≤z<1. Here, inthe nickel-based positive active material represented by ChemicalFormula 1, the nickel content may be greater than or equal to the cobaltcontent, and the nickel content may be greater than or equal to themanganese content.

In Chemical Formula 1, 0.95≤a≤1.3, for example, 1.0≤a≤1.1; 0<x≤0.33, forexample 0.1≤x≤0.33; 0≤y≤0.5, for example 0.05≤y≤0.3; 0≤z≤0.05; and0.33≤(1-x-y-z)≤0.95, for example 0.33≤(1-x-y-z)≤0.95.

For example, in Chemical Formula 1, 0≤z≤0.05, 0<x≤0.33, and 0≤y≤0.33.

For example, in Chemical Formula 1, (1-x-y-z)≥0.4, for example(1-x-y-z)≥0.5, or (1-x-y-z)≥0.6.

In some embodiments, in Chemical Formula 1, z may be 0.

In the nickel-based positive active material, the nickel content may begreater than or equal to about 0.5 mol %, for example, greater than orequal to about 0.55 mol %, or greater than or equal to about 0.57 mol %,and for example, less than or equal to about 0.95 mol %, less than orequal to about 0.9 mol %, less than or equal to about 0.8 mol %, lessthan or equal to about 0.7 mol %, less than or equal to about 0.65 mol%, less than or equal to about 0.63 mol %, for example, about 0.5 mol %to about 0.95 mol %, about 0.55 mol % to about 0.9 mol %, or about 0.57mol % to about 0.63 mol % based on a total amount of transition metals(Ni, Co, and Mn). In the nickel-based positive active material, thenickel content may be larger than each of the manganese content and thecobalt content.

In the nickel-based positive active material, the nickel content may belarger than the content of the other transition metals based on 1 mol(e.g. molar equivalent) of total transition metals. In this way, whenthe nickel-based positive electrode active material having a largenickel content is used as the first positive active material and thesecond positive active material, lithium diffusivity may be high,conductivity may be good, and a higher capacity at the same voltage maybe obtained when the rechargeable lithium battery employing the positiveelectrode including the same is used.

In some embodiments, a pressed density of the positive active materialfor a rechargeable lithium battery including the first positive activematerial and the second positive active material may be, for example,greater than or equal to about 3.2 g/cc, greater than or equal to about3.25 g/cc, greater than or equal to about 3.3 g/cc, greater than orequal to about 3.35 g/cc, or greater than or equal to about 3.4 g/cc. Insome embodiments, the pressed density of the positive active materialfor a rechargeable lithium battery may be obtained by inserting about 3g of the positive active material for a rechargeable lithium battery ina pressed density-measuring device and then, pressing it with a power ofabout 3 tons for about 30 seconds. Accordingly, the positive activematerial for a rechargeable lithium battery including the first andsecond positive active materials having different sizes according toembodiments of the present disclosure may secure a positive electrodehaving excellent electrode plate density.

Hereinafter, a positive active material for a rechargeable lithiumbattery according embodiments of the present disclosure is explained.

The positive active material for a rechargeable lithium batteryaccording to embodiments of the present disclosure includes the firstpositive active material including the secondary particle including atleast two agglomerated primary particles, wherein at least one part ofthe primary particles has a radial arrangement structure; and the secondpositive active material has the monolith structure. In someembodiments, the secondary particle may further include particles havinga monolith structure. For example, the positive active material may havesubstantially the same constitution (e.g., composition) as describedabove except that the secondary particle of the first positive activematerial may additionally further include particles having a monolithstructure.

In some embodiments, the particles having a monolith structure may beadhered or attached to an external part of the secondary particle,and/or in some embodiments, dispersed in an internal part thereof. Forexample, the particles having a monolith structure may be agglomerated(physically and/or chemically bound) to the secondary particle, or maynot be physically and/or chemically bound to the secondary particle butmay fill pores in the secondary particle and/or contact walls of thepores.

Hereinafter, referring to FIG. 4, a structure of a rechargeable lithiumbattery including a positive electrode including the positive activematerial for a rechargeable lithium battery according to embodiments ofthe present disclosure, and a method of manufacturing the rechargeablelithium battery are illustrated.

FIG. 4 is a schematic view showing a structure of a rechargeable lithiumbattery including a positive electrode including a positive activematerial for a rechargeable lithium battery according to embodiments ofthe present disclosure.

Referring to FIG. 4, a rechargeable lithium battery 21 includes apositive electrode 23 including the positive active material for arechargeable lithium battery, a negative electrode 22, and a separator24.

The positive electrode 23 and the negative electrode 22 may bemanufactured by coating a composition for forming a positive activematerial layer and a composition for forming a negative active materiallayer on each current collector, respectively, and drying the same.

The composition for the positive active material layer may be preparedby mixing a positive active material, a conductive agent, a binder, anda solvent, wherein the positive active material is the nickel-basedactive material represented by Chemical Formula 1.

The binder may help binding between the active materials, conductiveagent, and/or the like as well as binding these materials on a currentcollector, and may be added in an amount of about 1 to about 50 parts byweight based on a total weight of 100 parts by weight of the positiveactive material. Non-limiting examples of such a binder may includepolyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose(CMC), starch, hydroxypropyl cellulose, recycled cellulose,polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene,an ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, astyrene butadiene rubber, a fluorine rubber, various copolymers, and/orthe like. The amount thereof may be about 2 to about 5 parts by weightbased on a total weight of 100 parts by weight of the positive activematerial. When the amount of the binder is within this range, thebinding force of the active material layer to the current collector maybe suitable or good.

The conductive agent is not particularly limited as long as it does notcause a chemical change of a battery (e.g. an unwanted chemicalreaction), and has conductivity. Non-limiting examples of the conductiveagent may include graphite (such as natural graphite and/or artificialgraphite); a carbon-based material (such as carbon black, acetyleneblack, Ketjenblack®, channel black, furnace black, lamp black, summerblack, and/or the like); a conductive fiber (such as a carbon fiberand/or a metal fiber, and/or the like); carbon fluoride; a metal powder(such as an aluminum and/or nickel powder); zinc oxide, a conductivewhisker (such as potassium titanate, and/or the like); a conductivemetal oxide (such as a titanium oxide); and a conductive material (suchas a polyphenylene derivative, and/or the like).

The amount of the conductive agent may be about 2 to about 5 parts byweight based on a total weight of 100 parts by weight of the positiveactive material. When the amount of the conductive agent is within thisrange, the conductivity characteristics of the resultant electrode maybe improved.

Non-limiting examples of the solvent may be N-methyl pyrrolidone, and/orthe like.

The amount of the solvent may be about 1 part by weight to about 10parts by weight based on a total weight of 100 parts by weight of thepositive active material. When the amount of the solvent is within thisrange, the active material layer may be easily formed.

The positive current collector may have a thickness of about 3 μm toabout 500 μm. The material for the positive current collector is notparticularly limited as long as it does not cause a chemical change inthe battery (e.g. an unwanted chemical reaction) and has highconductivity, and may be for example, stainless steel, aluminum, nickel,titanium, heat-treated carbon, and/or aluminum or stainless steel thatis surface treated with carbon, nickel, titanium, and/or silver. Thecurrent collector may have fine irregularities formed on its surface toincrease adhesion to the positive active material, and may be providedin any suitable form (such as a film, a sheet, a foil, a net, a porousbody, foam, and/or a non-woven fabric body).

Separately, a negative active material, a binder, a conductive agent,and a solvent may be mixed to prepare a composition for a negativeactive material layer.

The negative active material may be or include a material capable ofintercalating and deintercalating lithium ions. Non-limiting examples ofthe negative active material may be a carbon-based material (such asgraphite and/or carbon), a lithium metal, an alloy thereof, a siliconoxide-based material, and/or the like. In some embodiments, siliconoxide may be used.

The binder may be added in an amount of about 1 part by weight to about50 parts by weight based on a total weight of 100 parts by weight of thenegative active material. Non-limiting examples of the binder may besubstantially the same as available for the positive electrode.

The conductive agent may be used in an amount of about 1 part by weightto about 5 parts by weight based on a total weight of 100 parts byweight of the negative active material. When the amount of theconductive agent is within this range, the conductivity characteristicsof the resultant electrode may be improved.

An amount of the solvent may be about 1 part by weight to about 10 partsby weight based on a total weight of 100 parts by weight of the negativeactive material. When the amount of the solvent is within this range,the negative active material layer may be easily formed.

The conductive agent and the solvent may use substantially the samematerials as those used in manufacturing the positive electrode.

The negative current collector may have a thickness of about 3 μm toabout 500 μm. The material for the negative current collector is notparticularly limited as long as it does not cause a chemical change inthe battery (e.g. an unwanted chemical reaction) and has highconductivity. Non-limiting examples may include copper; stainless steel;aluminum; nickel; titanium; heat-treated carbon; copper and/or stainlesssteel surface-treated with carbon, nickel, titanium, and/or silver; analuminum-cadmium alloy; and/or the like. The negative current collectormay have fine irregularities formed on the surface to increase theadhesion to the negative active materials, and may be provided in anysuitable form (such as a film, a sheet, a foil, a net, a porous body,foam, and/or a non-woven fabric body), similar to the positive currentcollector.

A separator may be between the positive electrode and the negativeelectrode, each being manufactured according to the above processes.

The separator may have a pore diameter of about 0.01 μm to about 10 μm,and a thickness of about 5 μm to about 300 μm. Non-limiting examples mayinclude an olefin-based polymer (such as polypropylene, polyethylene,and/or the like); and/or a sheet or a nonwoven fabric formed of a glassfiber. When a solid electrolyte such as a polymer is used as theelectrolyte, the solid electrolyte may also serve as the separator.

A lithium salt-containing non-aqueous electrolyte may be composed of anon-aqueous electrolyte and a lithium salt. The non-aqueous electrolytemay be a non-aqueous electrolyte, an organic solid electrolyte, or aninorganic solid electrolyte.

The non-aqueous electrolyte may be or include, for example, an aproticorganic solvent (such as N-methyl-2-pyrrolidinone, propylene carbonate,ethylene carbonate, butylene carbonate, dimethyl carbonate, diethylcarbonate, gamma-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide,N,N-dimethyl formamide, dioxolane, acetonitrile, nitromethane, methylformate, methyl acetate, phosphoric acid triester, trimethoxy methane,dioxolane derivative, sulfolane, methyl sulfolane,1,3-dimethyl-2-imidazolidinone, a propylene carbonate derivative, atetrahydrofuran derivative, ether, methyl propionate, ethyl propionate,and/or the like).

The organic solid electrolyte may be, for example, a polyethylenederivative, a polyethylene oxide derivative, a polypropylene oxidederivative, a phosphoric acid ester polymer, polyester sulfide,polyvinyl alcohol, polyvinylidene fluoride, and/or the like.

The inorganic solid electrolyte may be, for example, Li₃N, LiI, Li₅NI₂,Li₃N—LiI—LiOH, LiSiO₄, LiSiO₄—LiI—LiOH, Li₂SiS₃, Li₄SiO₄,Li₄SiO₄—LiI—LiOH, Li₃PO₄—Li₂S—SiS₂, and/or the like.

The lithium salt may be a material that is readily soluble in thenon-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO₄, LiBF₄,LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li,CF₃SO₃Li, (CF₃SO₂)₂NLi, lithium chloroborate, lower aliphatic lithiumcarbonates, tetraphenyl lithium borate, lithium imides, and/or the like.

The positive electrode 23, the negative electrode 22, and the separator24 are wound or folded and accommodated in the battery case 25. Then, anorganic electrolyte solution is injected into the battery case 25 andthe cap assembly 26 is sealed to complete the rechargeable lithiumbattery 21 as shown in FIG. 4.

The battery case 25 may have any suitable shape or form (such ascylindrical, prismatic, thin film, and/or the like). In someembodiments, the rechargeable lithium battery 20 may be a large-scalethin film-type battery. The rechargeable lithium battery may be alithium ion battery. A cell structure including a separator between thepositive electrode and the negative electrode may be formed. The cellstructure may be stacked in a bi-cell structure and then impregnatedwith an organic electrolyte solution, and the resulting product may beplaced in a pouch and sealed to manufacture a lithium ion polymerbattery. In some embodiments, a plurality of cell structures may bestacked to form a battery pack, which may be used in devices requiring ahigh capacity and a high power. For example, the battery pack may beused in a laptop, a smart phone, an electric vehicle, and/or the like.

In some embodiments, the rechargeable lithium battery may have improvedstorage stability, cycle-life characteristics, and high rate capacitycharacteristics at a high temperature, and may be used in an electricvehicle (EV). For example, it may be used in a hybrid vehicle such as aplug-in hybrid electric vehicle (PHEV).

The rechargeable lithium battery according to embodiments of the presentdisclosure may exhibit improved electrode plate density with respect tothe positive active material, and thus may have suitable electrochemicalcharacteristics for a rechargeable lithium battery.

In some embodiments, the rechargeable lithium battery according toembodiments of the present disclosure may have a minimized or reducedresidual lithium concentration in the positive electrode, minimizing orreducing the generation of gas in the cell through the reaction betweenthe residual lithium and the electrolyte solution, and thus may havehigh cell stability, and gelation caused by residual lithium may beminimized or reduced to form a stable positive electrode.

Hereinafter, a method of preparing the positive active material for arechargeable lithium battery according to embodiments of the presentdisclosure is described.

A method of preparing the positive active material for a rechargeablelithium battery according to embodiments of the present disclosure mayinclude forming a first nickel-based oxide using a first precursor and afirst heat treatment, obtaining a second nickel-based oxide using asecond precursor and a second heat treatment, mixing the firstnickel-based oxide and the second nickel-based oxide, and subjecting themixture in an oxidizing gas atmosphere to a third heat-treatment toobtain a positive active material including the first positive activematerial and the second positive active material. Hereinafter, themethod is explained in more detail.

First, the first precursor is subjected to a first heat-treatment underan oxidizing gas atmosphere to obtain the first nickel-based oxide.

In some embodiments, the oxidizing gas atmosphere may use an oxidizinggas (such as oxygen and/or air). The first heat-treatment may be, forexample, performed at about 800° C. to about 900° C. A time for thefirst heat-treatment may be selected according to the heat-treatmenttemperature and the like, and for example, may be about 5 to about 15hours. The first precursor according to embodiments of the presentdisclosure may include Li, Ni, Co, Mn, and optionally an elementselected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr),barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe),copper (Cu), zirconium (Zr), and aluminum (Al); the elements may beincluded in set or predetermined mole ratios, for example, within rangessatisfying each stoichiometric ratio.

In some embodiments, the first precursor may be obtained by mixing afirst composite metal hydroxide with a lithium-based material.

The first composite metal hydroxide may include at least nickel, and mayfurther include elements selected from the above group within a rangesatisfying a stoichiometric ratio, and the nickel and additionalelements may be bound to a hydroxyl group.

The lithium-based material may serve as a lithium source, so that thepositive active material for a rechargeable lithium battery according toembodiments of the present disclosure may function as a positive activematerial. The type or kind of lithium-based material according toembodiments of the present disclosure is not particularly limited andmay include, for example, Li₂CO₃, LiOH, a hydrate thereof, or acombination thereof.

In some embodiments, the second precursor, separately from the firstprecursor, may be subjected to a second heat-treatment under anoxidizing gas atmosphere. The resulting material may be pulverized toobtain the second nickel-based oxide including particles having amonolith structure. For example, the process of obtaining the secondnickel-based oxide may further include pulverizing the resultingmaterial obtained after subjecting the second precursor to the secondheat-treatment in an oxidizing gas atmosphere, the particles having amonolith structure

In some embodiments, the oxidizing gas atmosphere may use an oxidizinggas (such as oxygen and/or air). The second heat-treatment may be, forexample, performed at about 800° C. to about 1000° C. A time for thesecond heat-treatment may be selected according to the heat-treatmenttemperature and/or the like, and for example, may be about 5 to about 20hours. The second precursor may be obtained by mixing a second compositemetal hydroxide with the aforementioned lithium-based material.

The second composite metal hydroxide, may include Li, Ni, Co, Mn, andoptionally an element selected from boron (B), magnesium (Mg), calcium(Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium(Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); theelements may be included in set or predetermined mole ratios, forexample, within ranges satisfying each stoichiometric ratio. Theelements (including at least nickel and a hydroxyl group) may be boundin a range satisfying a stoichiometric ratio. An average particlediameter of the second composite metal hydroxide may be, for example,greater than or equal to about 0.5 μm, greater than or equal to about1.0 μm, greater than or equal to about 1.5 μm, greater than or equal toabout 2.0 μm, and for example, less than or equal to about 8 μm, lessthan or equal to about 7 μm, less than or equal to about 6 μm, less thanor equal to about 5 μm, or less than or equal to about 4 μm.

In some embodiments, the second composite metal hydroxide may have aspecific surface area of about 1 m²/g to about 30 m²/g, as measuredusing a BET method. For example, the specific surface area may be about2 m²/g to about 25 m²/g, for example, about 5 m²/g to about 25 m²/g.When the second composite metal hydroxide has a specific surface areasatisfying this range, the second nickel-based oxide may be pulverizedinto particles having a monolith structure within the above averageparticle diameter range during a pulverization process described below,thereby reducing an amount of residual lithium.

Subsequently, a mixture of the second composite metal hydroxidesubjected to the second heat-treatment and the lithium-based materialmay be pulverized to obtain the second nickel-based oxide including theparticles having a monolith structure within the above average particlediameter range. The second nickel-based oxide may have a smaller averageparticle diameter than the above first nickel-based oxide. Thepulverization may be performed using any suitable pulverizing device(such as a jet mill and/or the like).

The particles having a monolith structure and the average particlediameter range described above may not be agglomerated, but dispersed asdescribed above. The amounts and/or a mixing ratio of the lithium-basedmaterial and the second composite metal hydroxide are not particularlylimited, but may simultaneously (concurrently) be adjusted within asuitable range to minimize or reduce the amount of excess lithium saltand thereby the lithium-based material residue after preparing thenickel-based active material.

In some embodiments, a mole ratio (Li/Me) e.g., of lithium (Li) relativeto the remaining metal elements (Me) in the second precursor may be, forexample, greater than or equal to about 0.8, greater than or equal toabout 0.85, greater than or equal to about 0.9, greater than or equal toabout 0.95, or greater than or equal to about 1.0, and for example, lessthan or equal to about 1.05, less than or equal to about 1.04, or lessthan or equal to about 1.03.

In some embodiments, a mole ratio of Ni, Co, Mn, and additional selectedelements in the first composite metal hydroxide and the second compositemetal hydroxide may be freely selected within a range for preparing thenickel-based positive active material represented by Chemical Formula 1,but a mole ratio of Ni may be adjusted to be larger than the mole ratiosof Co, Mn, and the additional selected elements. In some embodiments,the second precursor according to embodiments of the present disclosuremay be adjusted to have the same mole ratio as the above firstprecursor.

Subsequently, the first nickel-based oxide may be mixed with the secondnickel-based oxide. In some embodiments, a mixing ratio of the firstnickel-based oxide and the second nickel-based oxide may be, forexample, about 9:1 to about 5:5, about 8:2 to about 5:5, about 8:2 toabout 6:4, or about 7:3 based on weight. When the mixing ratio of thefirst nickel-based oxide and the second nickel-based oxide satisfies theabove ranges, a positive active material for a rechargeable lithiumbattery may have a low residual lithium compound concentration, and mayalso secure excellent electrode plate density when used to manufacturean electrode plate.

Subsequently, the mixture of the first nickel-based oxide and the secondnickel-based oxide may be subjected to a third heat-treatment under anoxidizing gas atmosphere.

The oxidizing gas atmosphere may include an oxidizing gas (such asoxygen and/or air).

The third heat-treatment may be performed, for example, at about 800° C.to about 1000° C.

A time for the third heat-treatment may be selected according to theheat-treatment temperature and/or the like, and for example, may beabout 3 to about 10 hours.

When the heat-treatment is completed, the temperature may be cooled downto room temperature to prepare a positive active material for arechargeable lithium battery according to embodiments of the presentdisclosure. The positive active material for a rechargeable lithiumbattery may include the first positive active material including thesecondary particle including at least two agglomerated primaryparticles, along with the second positive active material having amonolith structure as described above, and at least one part of theprimary particles in the secondary particle may be arranged in a radialshape.

The above preparing method may provide a positive active material for arechargeable lithium battery within the above residual lithiumconcentration range without a residual lithium removal process (such asa separately additional washing process and/or the like). The positiveactive material and a rechargeable lithium battery including the samemay show excellent stability and electrochemical characteristics, asdescribed above.

Hereinafter, the embodiments are illustrated in more detail withreference to examples. These examples, however, are not in any sense tobe interpreted as limiting the scope of the disclosure.

EXAMPLE

1. Precursor Process

(1) Preparing Process of First Nickel-Based Oxide

A nickel-based active material precursor (Ni_(0.6)Co_(0.2)Mn_(0.2)OH)was synthesized using a co-precipitation method to prepare a firstnickel-based oxide. In the following preparing process, the nickel-basedactive material precursor was synthesized using a raw metal material(such as nickel sulfate, cobalt sulfate, and manganese sulfate).

First Act: 1.5 kW/m³, NH₄OH 0.30 M, pH 10 to 11, Reaction Time: 6 Hours

First, ammonium hydroxide having a concentration of 0.30 M was put in areactor. The raw metal material and a complexing agent were addedthereto at a rate of 90 mL/min and 10 mL/min, respectively, with anagitation power of 1.5 kW/m³ at a reaction temperature of 50° C. tostart the reaction.

The reaction proceeded for 6 hours, during which time NaOH was injectedto maintain pH. The core particles obtained from the reaction had anaverage size of about 5.5 μm to about 6.5 μm. The second act wasperformed as follows.

Second Act: 1.0 kW/m³, NH₄OH 0.35 M, pH 10 to 11, Reaction Time: 6 Hours

The complexing agent was maintained at a concentration of 0.35 M bychanging the addition rates of the raw metal material and the complexingagent to 100 mL/min and 15 mL/min, respectively, while the reactiontemperature was maintained at 50° C. The reaction proceeded for 6 hours,during which time NaOH was injected to maintain pH. Herein, theagitation power was adjusted to 1.0 kW/m³, which is lower than that ofthe first act. The particles having a core and a middle layer, asobtained from the reaction, had an average size of about 9 μm to about10 μm.

Third Act: 1.0 kW/m³, NH₄OH 0.40 M, pH 10 to 11, Reaction Time: 4 Hours

The addition rates of the raw metal material and the complexing agentwere changed to 150 mL/min and 20 mL/min, respectively, to adjust theconcentration of the complexing agent to 0.40 M, while the reactiontemperature was maintained at 50° C. The reaction proceeded for 4 hours,during which time NaOH was injected to maintain pH. Herein, theagitation power was maintained to be the same as in the second act.

Post-Processing

For post-processing, the resultant material was washed and dried withhot air at about 150° C. for 24 hours to obtain a nickel-based activematerial precursor.

Subsequently, the nickel-based active material precursor and LiOHparticles having an average size of about 10 μm were mixed in (at) amole ratio of 1:1 and subjected to a first heat-treatment under an airatmosphere at about 800° C. for 6 hours to obtain a first nickel-basedoxide (LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂).

The obtained first nickel-based oxide had an average particle diameterof about 12.5 μm.

(2) Preparing Process of Second Nickel-Based Oxide

Separately from the above, nickel sulfate (NiSO₄.6H₂O), cobalt sulfate(CoSO₄.7H₂O), and manganese sulfate (MnSO₄.H₂O) in a mole ratio of 6:2:2were dissolved in distilled water (as a solvent) to prepare a mixedsolution. An ammonium hydroxide (NH₄OH) dilute solution and sodiumhydroxide (NaOH) as a precipitator were prepared as precursors forforming a complexing compound. Subsequently, the raw metal materialmixed solution, the ammonia hydroxide, and the sodium hydroxide wereadded to a reactor. The obtained mixture was reacted for 15 hours whilebeing stirred. Subsequently, the obtained slurry solution in the reactorwas filtered, washed with distilled water having high purity, and driedfor 24 hours to yield a second composite metal hydroxide(Ni_(0.6)Co_(0.2)Mn_(0.2)OH)₂ powder. The second composite metalhydroxide powder had an average particle diameter of about 3.2 μm and aspecific surface area of about 13 m²/g as measured using a BET method.The second composite metal hydroxide powder and Li₂CO₃ were mixed tosatisfy a Li/(Ni+Co+Mn) ratio of 1.02, put in a furnace, and subjectedto a second heat-treatment under an air atmosphere at 910° C. for 11hours to obtain a second nickel-based oxide. Subsequently, the secondnickel-based oxide was pulverized for about 30 minutes and thenseparated/dispersed as a plurality of second positive active materialparticles having the above monolith structure.

2. Preparing Process of Positive Active Material

Subsequently, the first nickel-based oxide and the pulverized secondnickel-based oxide including the plurality of second positive activematerial particles having the monolith structure were mixed in a weightratio of 7:3, put in a furnace, and subjected to a third heat-treatmentunder an oxygen atmosphere at about 850° C. for 6 hours. Then, thefurnace was cooled down to room temperature to obtain a positive activematerial for a rechargeable lithium battery wherein the first and secondpositive active materials were mixed.

The positive active material for a rechargeable lithium battery was amixture of the first positive active material, (in which at least onepart of each of the primary particles was arranged in a radial shape andthe primary particles were agglomerated into a secondary particle) andthe second positive active material having a monolith structure, asdescribed above.

Comparative Example 1

A positive active material for a rechargeable lithium battery accordingto Comparative Example 1 was obtained according to substantially thesame method as in Example 1, except for not pulverizing the secondnickel-based oxide, and instead directly mixing it with the firstnickel-based oxide.

Comparative Example 2

A positive active material for a rechargeable lithium battery accordingto Comparative Example 2 was prepared according to substantially thesame method as in Example 1, except for using the second composite metalhydroxide having an average particle diameter of 3.2 μm and a specificsurface area of 33 m²/g measured using a BET method, and not pulverizingit after the second heat-treatment but instead directly mixing it withthe first nickel-based oxide.

Comparative Example 3

The first composite metal hydroxide, the second composite metalhydroxide, and lithium hydroxide (LiOH.H₂O) were mixed to satisfy aratio of Li/(Ni+Co+Mn)=1.02.

Subsequently, the mixed material was put in a furnace, subjected to afirst heat-treatment at about 850° C. for 6 hours, and then subjected toa second heat-treatment at the same temperature for 6 hours. The furnacewas cooled down to room temperature to obtain a positive active materialfor a rechargeable lithium battery according to Comparative Example 3.

Each positive active material for a rechargeable lithium batteryaccording to the Example and Comparative Examples was analyzed tomeasure the residual amount of Li₂CO₃ and LiOH and a concentration ofresidual Li, and the results are shown in Table 1.

The pressed densities of the each of the positive active materials for arechargeable lithium battery according to Example and ComparativeExamples were measured, and the results are shown in Table 1.

TABLE 1 Residual Residual Residual Li Pressed Li₂CO₃ LiOH concentrationdensity (wt %) (wt %) (ppm) (g/cc) Example 0.105 0.265 967 3.43Comparative 0.109 0.271 1000 3.22 Example 1 Comparative 0.116 0.277 10223.22 Example 2 Comparative 0.221 0.395 1542 3.19 Example 3

Referring to Table 1, the positive active material for a rechargeablelithium battery according to the Example showed overall small Li₂CO₃ andLiOH residue amounts and a low residual lithium concentration comparedwith the Comparative Examples and particularly, Comparative Example 3.On the other hand, Comparative Examples 1 and 2 generally showed asimilar residual lithium concentration.

The positive active material for a rechargeable lithium batteryaccording to the Example showed excellent pressed density compared withthe positive active materials according to the Comparative Examples. Thepositive active material for a rechargeable lithium battery according tothe Example showed a pressed density of about 3.43 g/cc, which is 70%higher than the theoretical density of about 4.8 g/cc of a positiveactive material having the same composition. Accordingly, the positiveactive material for a rechargeable lithium battery according to theExample may minimize or reduce a residual lithium concentration andsimultaneously (concurrently) have a low pressed density, and thus mayform an improved electrode plate compared with the positive activematerials according to the Comparative Examples.

Coin half-cells were manufactured using the positive active materialsaccording to each of the Example and Comparative Examples.

96 g of the positive active material secondary particles for arechargeable lithium battery according to each Example or ComparativeExample, 2 g of polyvinylidene fluoride, and 137 g ofN-methylpyrrolidone as a solvent, and 2 g of carbon black as aconductive agent were mixed and degassed using a blender to obtain asubstantially uniformly-dispersed slurry for a positive active materiallayer.

The slurry for a positive active material layer was coated on analuminum foil and thus formed into a thin electrode plate, dried at 135°C. for greater than or equal to 3 hours, and compressed and vacuum-driedto manufacture a positive electrode.

The positive electrode and a lithium metal foil as a counter electrodewere used to manufacture a 2032 type coin half-cell. A separator formedof a porous polyethylene (PE) film (thickness: about 16 μm) was placedbetween the positive electrode and the lithium metal counter electrode,and an electrolyte solution was injected thereinto to manufacture the2032 type coin cell. Herein, the electrolyte solution was prepared bymixing ethylenecarbonate (EC) and ethylmethylcarbonate (EMC) in a volumeratio of 3:5 and dissolving 1.1 M LiPF₆ therein.

The coin half-cells according to the Example and Comparative Exampleswere each charged using a constant current (0.1 C) and constant voltage(4.3 V, 0.05 C cut-off) condition, paused for 10 minutes, dischargeddown to 3.0 V under a constant current (0.1 C) condition, during whichthe charge/discharge capacity and efficiency of each of the coinhalf-cells were measured, and the results are shown in Table 2.

The specific charge and discharge capacities (mAh/g) were measured forthe coin half-cells using the positive active materials according to theExample or Comparative Examples, and multiplied by the compressiondensity (g/cc) to obtain a volumetric capacity (mAh/cc) for each of thecoin half-cells according to the Example and Comparative Examples, andthe results are shown in Table 2.

TABLE 2 0.1 C 0.1 C 0.1 C charge discharge charge/discharge Volumetriccapacity capacity efficiency Capacity (mAh/g) (mAh/g) (%) (mAh/cc)Example 199.0 179.3 90.1 615.0 Comparative 199.1 139.2 90.0 577.0Example 1 Comparative 198.9 181.7 91.4 585.1 Example 2 Comparative 197.9183.5 92.7 585.4 Example 3

Referring to Table 2, the coin half-cell according to the Example showedsimilar charge/discharge characteristics to the Comparative Examples,and accordingly, the nickel-based active material according toembodiments of the present disclosure may be used as a positive activematerial for a rechargeable battery.

However, the coin half-cell according to the Example showed a highvolumetric capacity compared with the Comparative Examples, andaccordingly, the positive active material for a rechargeable lithiumbattery according to embodiments of the present disclosure may provide arechargeable battery cell having excellent electrochemicalcharacteristics.

As used herein, expressions such as “at least one of”, “one of”, and“selected from”, when preceding a list of elements, modify the entirelist of elements and do not modify the individual elements of the list.Further, the use of “may” when describing embodiments of the presentdisclosure refers to “one or more embodiments of the presentdisclosure”.

In addition, as used herein, the terms “use”, “using”, and “used” may beconsidered synonymous with the terms “utilize”, “utilizing”, and“utilized”, respectively.

As used herein, the terms “substantially”, “about”, and similar termsare used as terms of approximation and not as terms of degree, and areintended to account for the inherent deviations in measured orcalculated values that would be recognized by those of ordinary skill inthe art.

Also, any numerical range recited herein is intended to include allsubranges of the same numerical precision subsumed within the recitedrange. For example, a range of “1.0 to 10.0” is intended to include allsubranges between (and including) the recited minimum value of 1.0 andthe recited maximum value of 10.0, that is, having a minimum value equalto or greater than 1.0 and a maximum value equal to or less than 10.0,such as, for example, 2.4 to 7.6. Any maximum numerical limitationrecited herein is intended to include all lower numerical limitationssubsumed therein and any minimum numerical limitation recited in thisspecification is intended to include all higher numerical limitationssubsumed therein. Accordingly, Applicant reserves the right to amendthis specification, including the claims, to expressly recite anysub-range subsumed within the ranges expressly recited herein.

While this disclosure has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the disclosure is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims and equivalents thereof.

DESCRIPTION OF SOME OF THE SYMBOLS

21: rechargeable lithium battery 22: negative electrode 23: positiveelectrode 24: separator 25: battery case 26: cap assembly

What is claimed is:
 1. A positive active material for a rechargeablelithium battery, comprising: a first positive active material comprisinga secondary particle comprising at least two agglomerated primaryparticles, at least one part of the primary particles having a radialarrangement structure; and a second positive active material having amonolith structure, wherein both of the first positive active materialand the second positive active material comprise a nickel-based positiveactive material.
 2. The positive active material of claim 1, wherein thesecond positive active material is included in an amount of about 10 wt% to about 50 wt % based on a total weight of the positive activematerial.
 3. The positive active material of claim 1, wherein: thesecondary particle comprises a radial arrangement structure, or thesecondary particle comprises an internal part comprising an irregularporous structure and an external part comprising a radial arrangementstructure.
 4. The positive active material of claim 1, wherein theprimary particles have a plate shape, and a long-axis of at least onepart of the primary particles is arranged in a radial direction.
 5. Thepositive active material of claim 1, wherein an average length of theprimary particles is about 0.01 μm to about 5 μm.
 6. The positive activematerial of claim 1, wherein an average particle diameter of the secondpositive active material is about 0.05 μm to about 10 μm.
 7. Thepositive active material of claim 1, wherein a residual lithiumconcentration in the positive active material is less than or equal toabout 1200 ppm.
 8. The positive active material of claim 1, wherein thefirst positive active material is represented by Chemical Formula 1:Li_(a)(Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z))O₂,  Chemical Formula 1 wherein, inChemical Formula 1, M is an element selected from boron (B), magnesium(Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium(V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum(Al), 0.95≤a≤1.3, x≤(1-x-y-z), y≤(1-x-y-z), 0<x<1, 0≤y<1, and 0≤z<1. 9.The positive active material of claim 1, wherein the second positiveactive material is represented by Chemical Formula 1:Li_(a)(Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z))O₂  Chemical Formula 1 wherein, inChemical Formula 1, M is an element selected from boron (B), magnesium(Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium(V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum(Al), 0.95≤a≤1.3, x≤(1-x-y-z), y≤(1-x-y-z), 0<x<1, 0≤y<1, and 0≤z<1. 10.A rechargeable lithium battery, comprising: a positive electrodecomprising the positive active material of claim 1; a negativeelectrode; and an electrolyte between the positive electrode and thenegative electrode.
 11. The rechargeable lithium battery of claim 10,wherein the second positive active material is included in an amount ofabout 10 wt % to about 50 wt % based on a total weight of the positiveactive material.
 12. The rechargeable lithium battery of claim 10,wherein: the secondary particle comprises a radial arrangementstructure, or the secondary particle comprises an internal partcomprising an irregular porous structure and an external part comprisinga radial arrangement structure.
 13. The rechargeable lithium battery ofclaim 10, wherein the primary particles have a plate shape, and along-axis of at least one part of the primary particles is arranged in aradial direction.
 14. The rechargeable lithium battery of claim 10,wherein a residual lithium concentration in the positive active materialis less than or equal to about 1200 ppm.
 15. The rechargeable lithiumbattery of claim 10, wherein the first positive active material isrepresented by Chemical Formula 1:Li_(a)(Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z))O₂,  Chemical Formula 1 wherein, inChemical Formula 1, M is an element selected from boron (B), magnesium(Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium(V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum(Al), 0.95≤a≤1.3, x≤(1-x-y-z), y≤(1-x-y-z), 0<x<1, 0≤y<1, and 0≤z<1. 16.The rechargeable lithium battery of claim 10, wherein the secondpositive active material is represented by Chemical Formula 1:Li_(a)(Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z))O₂  Chemical Formula 1 wherein, inChemical Formula 1, M is an element selected from boron (B), magnesium(Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium(V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum(Al), 0.95≤a≤1.3, x≤(1-x-y-z), y≤(1-x-y-z), 0<x<1, 0≤y<1, and 0≤z<1.